Table 1. Effects of cell density and conditioned medium on localization of Y-EI in E. coli BL21-DE3-ΔEI harboring the plasmid pRSETB-Y-EI.

	OD420			Punctate cells after incubation at 37°C, %
Exp.	Cells	Supernatant	Mixture	0 min	30 min	60 min	150 min
I	1	1	1.0	5	—	—	—
II	1	1	4.5	5	40	50	70
III	1	4.5	1.0	5	—	—	15-20 (4 h)
IV	1	4.5	4.5	5	—	70	—
V-VIII	4.5	1 or 4.5	1.0 or 4.5	70-80	—	—	—

E. coli BL21-DE3-ΔEI harboring pRSETB-Y-EI was grown overnight in Neidhardt medium containing 20 mM ribose and inoculated at a dilution of 1:100 into two 25-ml culture flasks. One contained 4 ml of the same medium with 1.89 mM ribose (culture 1); the second contained 20 mM ribose (culture 2). Growth was followed as described in the text. At stationary phase, culture 1 exhibited an OD₄₂₀ of 1.0, and culture 2 was at OD₄₂₀ of 4.5. After 7 h in stationary phase, 4-ml samples of the cultures were centrifuged, and the cells were separated from the supernatants. This gave four fractions: cells 1 and supernatant 1 from culture 1 and cells 4.5 and supernatant 4.5 from culture 2. Microscopic examination showed that the fluorescence in cells 1 was 95% diffuse and ≈5% punctate; cells 4.5 were ≈70-80% punctate and ≈20% diffuse. The cells were not washed but were resuspended to an OD₄₂₀ of 1.0 or 4.5 in supernatants 1 or 4.5 as specified. The suspension were shaken at 37°C, and aliquots were examined microscopically at the indicated times.

—, no change.